3.16.7-ckt25 -stable review patch. If anyone has any objections, please let me
know.
---8<------------------------------------------------------------
From: "Herton R. Krzesinski" <her...@redhat.com>
commit 2831c89f42dcde440cfdccb9fee9f42d54bbc1ef upstream.
This change fixes a bug for a corner case where we have the the last
release from a pty master/slave coming from a previously opened /dev/tty
file. When this happens, the tty->driver_data can be stale, due to all
ptmx or pts/N files having already been closed before (and thus the inode
related to these files, which tty->driver_data points to, being already
freed/destroyed).
The fix here is to keep a reference on the opened master ptmx inode.
We maintain the inode referenced until the final pty_unix98_shutdown,
and only pass this inode to devpts_kill_index.
Signed-off-by: Herton R. Krzesinski <her...@redhat.com>
Reviewed-by: Peter Hurley <pe...@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriq...@canonical.com>
---
drivers/tty/pty.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index e49616eeb1cc..5f37f0ddf7b9 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -617,7 +617,14 @@ static void pty_unix98_remove(struct tty_driver *driver,
struct tty_struct *tty)
/* this is called once with whichever end is closed last */
static void pty_unix98_shutdown(struct tty_struct *tty)
{
- devpts_kill_index(tty->driver_data, tty->index);
+ struct inode *ptmx_inode;
+
+ if (tty->driver->subtype == PTY_TYPE_MASTER)
+ ptmx_inode = tty->driver_data;
+ else
+ ptmx_inode = tty->link->driver_data;
+ devpts_kill_index(ptmx_inode, tty->index);
+ iput(ptmx_inode); /* drop reference we acquired at ptmx_open */
}
static const struct tty_operations ptm_unix98_ops = {
@@ -708,6 +715,15 @@ static int ptmx_open(struct inode *inode, struct file
*filp)
set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
tty->driver_data = inode;
+ /*
+ * In the case where all references to ptmx inode are dropped and we
+ * still have /dev/tty opened pointing to the master/slave pair (ptmx
+ * is closed/released before /dev/tty), we must make sure that the inode
+ * is still valid when we call the final pty_unix98_shutdown, thus we
+ * hold an additional reference to the ptmx inode
+ */
+ ihold(inode);
+
tty_add_file(tty, filp);
slave_inode = devpts_pty_new(inode,
